A multiple-cylinder internal combustion engine of the counterflow type has the intake and exhaust ports of the power cylinders located on one side of the cylinder head of the engine. Serious space requirements are involved in an internal combustion engine of this type and, to overcome such requirements, a multiple-cylinder internal combustion engine of the counterflow type has intake and exhaust manifolds which partake common mounting bolts each connecting a branch portion of the intake manifold and a branch portion of the exhaust manifold to the cylinder head. Problems are, however, still encountered in an internal combustion engine of this nature and, thus, an object of the present invention is to provide a useful solution to these problems.